Fibrosis of the bone marrow (myelofibrosis or MF) is a common pathologic feature of hematologic myeloproliferative disorders (MPD). It is associated with a dysregulated excessive or dysplastic production of blood cells driven by the gain-of-function mutations. While the common mutation of MF has been identified and the mutation profile is relatively uniform across most patients, the clinical outcomes vary substantially. It has been observed that patients with MPD are characterized by a systemic inflammatory response notable for high levels of circulating pro-inflammatory cytokines, which are highest in MF and associated with enlarged spleen (splenomegaly) and reduced overall survival. It is believed that cytokine-secreting cells in the bone marrow compartment ar mechanistically linked to pathogenesis and therapeutic response of MF. We hypothesize that detecting these cells and their cytokine functions can detect MF at earlier stages and potentially predict the likelihood of malignant progression to leukemia or therapeuticall reversing the pathological condition in patients. Yet, there are significant challenges n the clinic settings including the large degree of cellular heterogeneity in the bone marro compartment, the wide spectrum of cytokine functions on the individual cell basis, and the inability to conduct informative molecular measurement from limited quantitates of bone marrow biopsy specimens. This application aims to apply a microchip technology for single-cell, highly multiplex ( up to 42) cytokine assay to examine the cytokine functions of hematopoietic cells in bone marrow or even blood from patients with MF. This technology uniquely addressed the aforementioned challenges via micro engineering. We have demonstrated informative cytokine functional profiling in individual bone marrow cells from MF mouse models. In this work, we propose to develop new methods based on this platform to detect and measure myelofibrosis in human. Specifically, we will detect (1) cytokine secretion in blood and bone marrow cells from MF patients, (2) compare single-cell cytokine profiles between patients with polycythemia vera (PV), essential thrombocytosis (ET) and MF to distinguish non-fibrotic and fibrotic disease states, and detect abnormal cytokine-secreting hematopoietic cells in blood to monitor for MF progression. Ultimately, it has the potential to result in a clinically practical tool for early diagnosis, therapeutic stratification, and monitoring of human myelofibrosis.